Sex/gender differences exist in human cardiac disease resulting from many disease etoilogies including hypertension, myocardial infarction, and hypertrophic cardiomyopathy (HCM). The hearts of women with these disorders maintain, at least, adequate cardiac function whereas men typically demonstrate increased chamber dilation and wall thinning, all signs of progressively deteriorating cardiac disease. Humans with HCM caused by an autosomal dominant mutation (R403Q) in the predominant motor protein in the heart (1-myosin heavy chain) show a similar sex difference in cardiac disease progression. Like their human counterparts, male mice expressing the R403Q mutation in the heart develop HCM characterized by progressive left-ventricular dilation and cardiac dysfunction whereas females show hypertrophy without dilation or dysfunction. However, the mechanisms that underlie these differences remain unknown. Because the R403Q mutation resides in the motor protein of the cellular contractile apparatus, hearts expressing the R403Q mutation are energy deprived and that this may be due to the increased energetic cost of contraction when expressing the R403Q mutation. Therefore, the prediction is that the observed sex difference may result from the inability of male hearts to match this increased energetic demand compared to females. In support of this idea, male R403Q hearts show metabolic abnormalities consistent with an energy-deprived state. Adenosine monophosphate-activated kinase (AMPK) may be a central regulator of this sex difference because of its established role in (1) sensing changes in cellular energy state, (2) regulating mediators of energy producing pathways, and, (3) directly modifying contractile proteins by phosphorylation. Yet, no studies have systematically addressed AMPK sex dimorphisms in mice with the R403Q mutation. Therefore, the outlined experimental plan is designed to concisely test the hypothesis that male hearts do not adapt appropriately to the increase in energetic demand caused by the R403Q HCM mutation, which leads to progressively worsening cardiac dysfunction. The hypothesis to be tested is that the key mechanism that underlies this sexual dimorphism is an altered AMPK signaling axis in males compared to females. Moreover, these studies will provide a critical foundation upon which to guide future research into defining fundamental differences in metabolic and oxidative capacities of male and female hearts in order to more completely elucidate sex differences in cardiovascular disease etiology and treatment in the human population.